The present invention relates to a device for inductive energy transmission, and to a method for operating a device for inductive energy transmission.
Electric vehicles and plug-in hybrid vehicles, which are driven entirely or at least partially by means of electric motors, are known. The electrical energy here for driving the electric motor is provided by an electric energy store, for example a traction battery. Different approaches are taken to charging this energy store.
It is, for example, possible to connect the electric vehicle conductively to a charging station by means of a suitable charging cable. A user must establish an electrical connection between the electric vehicle and the charging station for this purpose. This can be found to be uncomfortable, in particular under bad weather conditions such as rain. As a result of the highly restricted electrical range of electric and plug-in hybrid vehicles, this cable connection must, moreover, be established by the user very often, which is felt by many users to be a significant disadvantage of electric vehicles in comparison with conventional vehicles.
Cable-free solutions for transmitting energy between the charging station and the vehicle therefore also exist. The energy is here transmitted from the charging station to the vehicle via an alternating magnetic field. The energy from the alternating magnetic field is converted in the vehicle into electrical energy, and the electrical energy passed to the energy store of the vehicle. With this solution it is, however, necessary for the vehicle to be arranged as precisely as possible over the charging station. Depending on the distance and alignment of the primary coil in the charging station and the secondary coil in the vehicle, different effects arise in the cable-free charging system. The coupling factor of the coil system can thus vary strongly. In this case there is a risk that the charging system is not operated at an optimum working point, which usually leads to a lower efficiency and/or a higher alternating magnetic field in the air gap between the primary coil and the secondary coil.
Document DE 10 2010 055 696 A1 discloses a system for contact-free transmission, wherein the frequency of the transmission system is adjusted on the primary side depending on state magnitudes of the secondary side. In addition to a pure adjustment of the system parameters on the primary side, it is additionally also possible to adjust the operating point of the inductive charging system through a power regulation on the secondary side or on both sides. A system of this type is described, for example, in document US 2011/0231029 A1, wherein an additional voltage converter is required on the secondary side.
There is also therefore a need for an inductive energy transmission that permits an improved adjustment of the energy transmission in the presence of variable coupling factors. There is, moreover, a need for an efficient and economical implementation of an inductive energy transmission with variable coupling factors.